1. Field of the Invention
The present invention relates to a rotation mechanism adapted to permit selective orienting adjustments of a rotatable seat provided in a vehicle such as a bus for orienting the seat towards a desired direction.
2. Description of the Prior Art
Various rotatable seats for use in a vehicle seat have been known, and also a variety of rotation mechanisms therefor have been devised and proposed.
As to the hitherto rotation mechanisms of this kind, the structure thereof is, by way of example, such that a sliding frame bearing a seat is slidably supported by a slide rail assembly fixed on the floor of a vehicle for transverse sliding movement relative to the vehicle body and is further provided with a rotation disc in a rotatable manner, on which rotation disc, a frame of the seat is fixed, and that the rotation disc is at its rear side connected with a displacing means having a plurality of rollers which are in rolling contact with a cam provided on the slide rail assembly. The movement of the displacing means along the cam causes the seat to rotate and move laterally of the vehicle, simultaneously, for changing the orientation of the seat.
This is disclosed from the Japanese Patent Publication No. 61-20451 and the Japanese Laid-Open Publication No. 56-131433, for instance.
However, those prior arts have been found disadvantageous in that the rotation of the seat for its orientation change requires a large labor and force on the part of an occupant sitting thereon and in most cases it is not easy or quite difficult for him or her to change the seat direction. With regard to the former Japanese prior art (61-20451), the displacing means are described as being a cross-shaped rotary cam with its four projecting ends being formed in a T-shaped configuration and two rollers are provided in an opposedly spaced manner so that each of them is located at a point to hinder the projecting ends of the cam, and consequently, the change of the seat direction requires a large operating force on the part of the occupant sufficient to rotate the seat in order for the T-shaped ends of the rotary cam to ride over the rollers. The same goes for the latter Japanese prior art (56-131433), in which the displacing means described as a roller and a triangle-shaped cam, is provided such that the roller is in rolling contact therewith, thus resulting in the necessity for the occupant to rotate the seat with a large force so as to cause the roller to roll over the vertex of the triangle-shaped cam.